Ceramic blade for turbine engine



Aug. 9, 1955 Filed Dec. 29, 1949 INVENTOR ATTORNEYS United StatesCERAMIC BLADE FOR TURBINE ENGINE Christian Schtirner, Augsburg, Germany,assignor to Maschinenfabrik Augsburg-Numberg A. G., Augsburg, Germany, acorporation of Germany Application December 29, 1949, Serial No. 135,580Claims priority, application Germany July 19, 1949 4 Claims. (Cl.253-77) This invention relates to a moving blade for turbine engines,more particularly, gas turbines, of ceramic masses.

Ceramic blades are adapted to substantially improve the thermalefficiency of internal combustion plants, e. g., exhaust gas turbines,without requiring complicated methods for cooling the constructionalelements owing to the increased working temperatures. Their low pricealso is an advantage. Of course, a ceramic blade is exposed to very highmechanical stresses, apart from the required insensitivity to changes oftemperature and the usual requirements as regards high speed, capacity,etc. However, the blade shapes cannot be simplified as much as it wouldbe desirable for the ceramic material, and the tensions resulting by thefiring and shrinking as a consequence of the requisite shapes, call formeasures for improving the rated fatigue limit. For fixing the blades inthe wheel body of steel (with due regard to the requirements for a tightmutual engagement of the seating surfaces irrespective of the differentheat expansions) approximately axially directed wedge-shaped grooveshave proved good, in which the complementarily shaped dovetail roots ofthe blades are seated. However, in order to ensure an efficient guidanceor conversion of the gas in the blade grid, relatively wide blades arerequired in order that a suficient strength may be left for the roots ofthe blades at the rim of the rotor between the grooves. These wideblades with their substantialy curved and partly even twisted surfaces,however, contrast with the straight roots of the blades which engage inthe wedge-shaped grooves of the rim of the rotor. Substantial parts ofthe blade project beyond the base of the root of the blade, wherebyceramic structures are resulting which are particularly unfavorable asto their mechanical rated fatigue limit.

It is the object of the present invention to improve the strength of theceramic blades.

With this object in View, according to the present invention the vane issubdivided in its width and the roots of the two blade elements havedifferent inclinations with respect to the circumferential direction ofthe wheel body in conformity with the average inclination of theskeleton line of these blade elements. Thus the blade portion of thesingle vane element becomes smaller in width. The resulting componentsof the profile are less and more uniformly curved and the appertainingroot portions with their plane wedge shape can be better adaptedthereto. The more gradual transition from the blade portion to the rootportion which is thereby ensured, no matter whether the blade isproduced by casting or by pressing, is favorable for a high ratedfatigue limit, since the preliminary tensions produced in theconstructional element by the firing and shrinking are thereby reduced.Owing to the more shallow curvature the preliminary tension at thetransition to the root portion is also reduced, and the measures of theprofile can be more accurately adhered to. The partial profiles can bejoined in such a way without expensive mechanical 2,715,0ll PatentedAug. 9, 1955 ice working that discontinuities in the curvature of theprofile are avoided. Also the staggering between the partial profilescan be chosen in such a way that no substantial leakage will resultbetween the front and rear faces of the blade. Finally also the lift ofthe profile is not substantially affected, since energy will be fed tothe field of vorticity at the back of the tail through a possible joint,so that the excess velocity will fade at the end of the back contour ofthe thick inlet or leading part of the blade.

Other and further objects, features and advantages of the invention willbe pointed out hereinafter and appear in the appended claims forming apart of the application.

In the accompanying drawing a now preferred embodiment of the inventionis shown by way of illustration and not by way of limitation.

In the drawing:

Fig. 1 is a side view of a subdivided or split blade,

Fig. 2 is a development of the rim of a rotor with a subdivided blade,

Fig. 3 is a fragmentary rear view, in the direction A, on the rotor asper Fig. 2, and

Fig. 4 is a development of the rim of a rotor with an undivided blade inaccordance with the conventional design.

Similar reference numerals denote similar parts in the different views.

It Will be seen from Fig. 2 that the joint '7 extending through the vaneportions 1, 2 and the root portions 8, 9 of the blade advantageouslydoes not form a plane but is staggered as indicated by the line 7. Therotor may also be subdivided, in the form of two halves 10, 11, on theline 7, or it may be made in one piece. Since the profile of the bladenear the root (Fig. 2) consists of a thick leading element 1 with acenter line of the profile of a practically axial direction and a thintail element 2 with a center line on the profile which is ratherinclined, at an angle a, with respect to the axial direction, the widthsa1, cm of the companion wedge-shaped root portions 8 and 9 may bedifferent. The advantage of the subdivision of the blade in accordancewith the invention will be realized particularly clearly by comparisonwith a through-going wedge-shaped root having a width and an averageinclination 61 to the circumferential direction as per Fig. 4, whichangle e1 is smaller than the angle a. In this case, freely overhangingportions 3 and 4 of the blade are present at the thick leading part ofthe profile and at the thin tail part 13 thereof, respectively, whichoverhanging portions are difficult to evaluate as to their stress, beingmoreover at a disadvantage as to their strength and liable to be damagedby their protruding position. In the blade according to the invention,on the contrary the whole vane part of the blade falls within animaginary radially directed prism whose base is formed by the companionroot portion of the vane.

Also, the conventional design presents corner portions 5 and 6 of thewedge-shaped root which are less utilized as to their strength, and asmaller tensile cross section of the wedge-shaped heads 12 of the rotorbetween the dovetail grooves 13 therein.

While the invention has been described in detail with respect to a nowpreferred example and embodiment of the invention it will be understoodby those skilled in the art after understanding the invention, thatvarious changes and modifications may be made without departing from thespirit and scope of the invention and it is intended, therefore, tocover all such changes and modifications in the appended claims.

Having'thus described 'my invention, I claim as new and desire to secureby Letters Patent? 1. In a gas turbine having-,a metal rotor and aplurality of composite ceramic blades mounted around the rim thereof,the combination Which ',comprises a plu-, ralityof transverse grooves inthe rim of said rotor for receivin'g said' blades, eachof said grooveshavinga portion disposed 'substantially'axially of said rotor and asecond portion disposed 'at an angle" to said axial IP01:

tion, a plurality, of separateceramic blade elements .a

assembled in edge-to-edge arrangement on said rotor forming eachfsaidblade,'.each of said elements having a vane part and a root part whichcompletely underlies the entire cross section of said vane part, meansfor aflixin'g the root, part of one; of .said elements, in said axial.portion ofijsaid "groove .in' said rotor, and means foratfixing therootpart ofanother of said elements in said second portion of said groove,the vane parts of saidassembled elements forming for each said blade acontinuous curved working surface and the rootpartsof I saidelementsab'utting ata substantial anglejandhaving a substantiallyrectilinear transverse cross section.

2. "In a gas turbine having a metal rotor and a ,plurality of. compositeceramic blades mounted around the rim thereof,"the combination, whichcomprises a plurality of transverse grooveshaving a substantiallyrectilinear, transverseaxial cross section in,the rim of t said rotorfor receiving said blades, each of said grooves having a first portionand a second portion which meets said 'first portion at an angle, aplurality of separate ceramic blade elements assembled in edge-to-edgearrangernent on said rotor forming each said blade, each of i'saidelements having a vane part and a root part which completely underliesthe entire .cross section of said yane part, meansfor afiixing the rootpart of one of saidf'elements in said,first portion of saidjgroove insaid rotor, means for affixing the rootpart of another of said 'elementsin said.second portion of said groove,

and corresponding projections and depressions on adjacent radial meetingedges of said elements forming staggered joints between said elementsineach said blade,

the vane parts of said assembled elements forming for each "said blade,a continuous working surface having a substantial curvature and (theroot parts of said elements abutting at an angle'andhaving asubstantially rectilinear 5 transverse cross section.

3;In' a gas turbine having'a metal rotor and a plu rality of compositeceramic blades mounted around the rim thereof, the combination whichcomprises a plurality of substantially transverse grooves in the rim ofsaid rotor forrrc e vi g sa d.b a es, hlofis i igrp v ha e a ing, afirstp rti nand a sccondhportionwhich meets said, t p on. t, an, v r gleta pu ality f parat a c.

l de. el me s a semb ed. in dg rt -e gq rr ngemen on said-rotor formingeachfiaid ,blade, -ea,C 1 of said ele: mentshaving a yane part and?,root part ,Which .corn

pletely underlies, the. entire. ,cross section of .said vane P m an f r.flix n the r p rt, of: on f, id 161 ments. in said first portion of saidgroove in saidrotor, meansfor afii'xing-flhe, rootpart of another, ofsaid elements said second ,portionpf; saidgroove, and co operatingprojections: and depressions on adjacent; meet,- dsesot i flidflane,partsforming, staggered joints, be-

tween said elements in each said blade substantially radially of saidrotor, the vane parts of said assembled elements forming for each saidblade a continuous working surface having a substantial curvatureradially outwardly of said rotor and the root parts of said elementsabutting at an angle and having a substantially rectilinear transversecross sectiomthe aggregate axial cross-sectional areas of said rootparts in each said blade being sub- 'stantially lessthan the area of arectangle underlying the entire curvature ,of '1 said assembled vaneelements ;providing increased rotor. rimsurface between saidzblades.

4. Ina, gas turbine having a metal rotor and a plurality of compositeceramic blades mounted around the rim thereof, the combination whichcomprises a plurality of transverse grooves in the rim of said rotor forreceiving said blades, each'of said grooves having a portion disposedsubstantially axially of said rotor and a second portion. disposed at asubstantial angle to the axisof said .rotor, a plurality. of separatecerami blade elements,

including a leading element and a tail element assembled in ,edgeto-edge; arrangement: on said rotor forming each said blade, each ,ofsaid elements having ;a vanepart and,

a root .partv whichcompletely; underlies the. entire cross section ofsaidyanepart, means including a trapezoidal configurationmfsaid root.part formounting the: root, part ofzsaid lead ng element. in saidaxialliportion of said a groove in said rotor, means including atrapezoidal configuration. of saidroot part for mountingtherootpart ofsaid tail element in saidsecondportion of said groove,

and cooperating projections and depressions on adjacent;- radial meetingedgesof said elements forming staggered joints, therebetween in eachsaid blade v substantially ra-a dially of said-rotor, the vane-parts ofsaid assembled, elements forming for each, said blade a continuouswork-,

ing. surface having I substantial curvature ,and the root parts of.said,elements abuttingt at, an angle, and the rag-, gregate. axial,cross-sectional areaof said root .partsin each said blade beingsubstantially less than, the area; of a rectangle enclosing said entiresubstantialtcurvature of,

saidassembled vane parts providing increased rotor rim surface betweenadjacent said blades.

References Cited in the fileofthis patent UNITED STATES PATENTS OTHERREFERENCES Ser. No.,,385,333, Schutte (A. P. C.),, published,May-- Ser.No, 385,334, Schutte V-(A. P.- 0.), published May

